Microwave switches are used in redundant switching networks on spacecrafts to route M input signals to M outputs through N failure-prone devices, such as traveling wave tube amplifiers (TWTAS). This is accomplished using two layers of microwave switches, with each layer including M serial connected 4-port switches, for example, T-switches. The switches in the input layer are controlled to route the M input signals around the failed devices and through functioning devices. The switches in the output layer are controlled to route the signals produced by the M selected devices to the M outputs.
Typically, planar T-switch configurations are used effectively in redundant switching networks on board spacecraft. However, there are a number of drawbacks associated with the prior art switches. A typical spacecraft employs several hundred microwave switches so that a small reduction in the weight of each switch can result in significant cost savings.
The actuators are the primary weight components of the switches, and therefore a switch configuration having a simpler and lighter weight actuator is desirable. Further in a planar T-switch, the three inner and outer waveguides necessarily have different lengths. As a result, the signal paths through different ports have different microwave properties, which prohibits the overall system from being optimized. In addition, the ends of the center conductors are flared substantially to ensure contact to the underlying conductive reeds in the actuators. This limits the high frequency performance of the switch. Also in a planar T-switch, the physical access to the coaxial connector is limited. Finally, as the complexity of the redundant switching networks increases, it may be difficult to develop planar microwave switches with enough ports to reroute the signals.
The prior art encompasses a dual T-switch assembly that consists of two T-switches with a coaxial cable running between them. When connected together, a signal going into one switch can be passed through intermediate switches to any output. To accomplish this the assembly requires twelve signal paths, eight connectors and a coax cable. This configuration adds unnecessary weight and complexity to the switch assembly. The complexity of the system also results in diminished RF performance.
Pat. No. 5,936,482 provides a lighter weight three dimensional microwave switch that has improved uniformity between signal paths, high frequency performance and physical access. The switch configures the waveguide transmission lines in three dimensions to define a polyhedron and positions the I/O microwave ports at the corners of the polyhedron. An actuator selectively moves respective reeds in the waveguide transmission lines between a signal-attenuating position abutting the interior surface of the waveguide transmission line and a signal-conducting position substantially coaxial with the waveguide transmission line and abutting the signal lines of the I/O microwave ports coupled to opposite ends of the waveguide transmission line.
The three dimensional switch may have an octahedral cavity providing six (6) connectors and twelve (12) paths. Although the octahedral configuration requires an independent actuator for each path, it retains the microwave performance advantages of identical path lengths and configuration while reducing weight and simplifying the microwave path.
The three-dimensional switch proposed in Pat. No. 5,936,482 is lighter in weight and more reliable in performance than prior art microwave planar switches. However, it still has a complex interconnection arrangement that requires coax cables to connect switches. In addition, the three-dimensional switch has somewhat limited signal path flexibility.
There is an ever present need for reduced weight in spacecraft applications and improved RF performance. There is also a need for simplified switch interconnection methods and increased signal path flexibility over the prior art.